1. Field of the Invention
The present invention relates to a method for manufacturing a micromechanical diaphragm structure having access from the rear of the substrate, as well as a corresponding semiconductor component.
2. Description of Related Art
In manufacturing sensor elements for measuring relative pressure or differential pressure, access to the diaphragm structure from the rear is usually provided, this access enabling pressure to be applied to both sides of the sensor diaphragm. However, sensor elements for measuring absolute pressure are also provided with rear access for defined applications to apply pressure to the sensor diaphragm. When using an absolute pressure sensor in so-called “harsh environments,” this may avoid the front of the chip coming into contact with the measuring medium.
A method for manufacturing a semiconductor component having a diaphragm structure and rear access to this diaphragm structure is described in published German patent application document DE 10 2004 036 035 A1. The known method is based on a p-doped monocrystalline Si substrate. A contiguous, lattice-type area of the substrate surface is initially provided with n-doping. A substrate area beneath the n-doped lattice structure produced thereby is then porously etched, the n-doped lattice structure not being attacked by this etching process. In a subsequent epitaxy process, a closed monocrystalline Si epitaxial layer is then created on the n-doped lattice structure.
In a first variant of the known method, the porous silicon is rearranged during the epitaxy process and a further tempering step in such a way that a cavity is produced beneath the n-doped lattice structure and the epitaxial layer grown thereon.
In a second variant of the known method, a cavity is created beneath the n-doped lattice structure prior to the epitaxy process. In this variant, the cavity wall—as far as it is present prior to the epitaxy process—is protected by a thermal oxide against the growth of silicon material during the epitaxy process. Due to a corresponding process control, the epitaxial layer also grows laterally on the lattice structure, closing the lattice openings and thus also the cavity. These areas of the epitaxial layer complete the cavity wall and are not coated with oxide—according to the process control.
A third variant of the known method provides that the porous silicon beneath the n-doped lattice structure is oxidized to prevent the porous silicon from being rearranged during epitaxy. The cavity in this case is created only after the epitaxial layer is applied, by removing the porous silicon oxide. This may be done either via an access opening, which is subsequently introduced into the epitaxial layer, or via an access hole in the rear of the substrate, which may then also be used as a rear access to the diaphragm structure.